Ethylene-propylene copolymers (EPM) and ethylene-propylene-diene terpolymers (EPDM) are extensively utilized in a variety of applications. A particular application wherein EPM and EPDM are preferred because of their excellent physical properties, weathering and heat aging resistance, is in rubber sheeting, such as roofing, agricultural pond liners and water distribution membranes. EPM and EPDM sheeting materials usually are prepared by compounding the EPM, EPDM or mixtures thereof with the appropriate fillers, plasticizers, antidegradants, etc. in a suitable internal mixer, and calendering the resulting compound into the desired sheet rubber.
Because of outstanding weathering resistance and flexibility, cured elastomeric roof sheeting has been rapidly gaining acceptance. This material normally is prepared by vulcanizing the composition in the presence of sulfur or sulfur containing compounds such as mercaptans. Our earlier U.S. Pat. No. 4,803,020 also teaches the use of radiation crosslinking promoters in an EPDM sheeting composition which can be cured by ionizing radiation. Vulcanization and curing can be done in the presence of other compounds as well. For example, ethylene-butene copolymers may be cured in the presence of a triazine or organic peroxide.
Notwithstanding the usefulness of radiation curing, sulfur curing, and triazine curing, a disadvantage of utilizing these elastomers is the lack of adhesion of these elastomers, especially cured olefinic elastomers to themselves. This is a serious problem because in applying elastomeric sheets to a roof, it is usually necessary to splice the cured elastomeric sheets together. This splice or seam area is subjected to both short-term and long-term stresses such as those caused by roof movement, heavy winds, freeze-thaw cycling and thermal cycling. Such stresses may manifest themselves in shear forces or peel forces, i.e., the seam peels back under severe stress conditions or results in a partially open seam (often referred to as a fish-mouth condition) under less severe conditions. Suffice to say, it is necessary that the adhesion of the roofing membrane to itself be considered in order to develop good seams.
Notwithstanding the problem of adhesion, the elastomeric roof sheeting materials also lack flame and bum resistivity. In order to improve flame resistivity of the product using the olefinic elastomers, fillers such as antimony trioxide, decabromo diphenyl oxide (DBDPO), dechlorane (chlorinated alicyclic hydrocarbon) alumina trihydrate, and chlorinated or brominated paraffins, are normally incorporated into the composition as shown in U.S. Pat. Nos. 4,839,419 and 4,851,463. However, the capacity of these membranes to accept these flame retardant fillers is somewhat limited, especially with membranes which exhibit thermoplastic characteristics.
Furthermore, U.S. Pat. No. 4,801,639 relates to flame retardant olefinic resin compositions which comprise a mixed resin of olefin and a silane-grafted polymer, a hydrated metal compound and a dicarboxylic acid or dicarboxylic acid anhydride derivative.
Therefore, while the use of flame retardant additives offer effective means of increasing flame resistivity, if the use of flame retardant additive could be reduced or eliminated, the additional labor and material costs and related hardware necessary to incorporate the additive would effect a significant cost savings. Moreover, elimination of the need to employ more expensive crystalline and semi-crystalline elastomers would also be advantageous. Also, a need for elastomeric roofing material with improved burn resistivity without sacrifice of seam strength continues to exist.